1. Field of the Invention
For many years tin plated steel cans were the containers of choice in the canning of comestibles, and in fact, are still in extensive use today. However, competition from the aluminum industry has resulted in the use of aluminum cans for the packaging of many foods and beverage products previously the domain of the tin plated steel can. The present economics favor the aluminum can, due to the high cost and periodic scarcity of tin.
Accordingly, a need has arisen for steel cans without a tin coating for use in the comestible industry. Chromium (chromium/chromium oxide) coated steel, which resists undercutting of the lacquer or other outer finishings when defects in the finishing are present cannot however be used in the formation of drawn and ironed cans using present manufacturing equipment. In addition, even if a process could be found to form such chromium coated steel cans, chromium is not too satisfactory a metal on which to apply a finishing coating such as paint or lacquer, since adhesion qualities are not good and decrease rapidly as the thickness of the chromium coating increases.
Drawn and ironed steel cans, usually referred to as "black-plate" cannot be used for comestibles since defects in the finishing coatings would permit rusting and attack on the steel by the contents of the can, rendering the food or beverage contaminated with the steel metal, resulting in a metallic taste and off-color, and in extreme cases resulting in eventual weakening or penetration of the walls of the can on extended storage. In addition, rusting of the clean cans prior to the application of the finishing coating cannot readily be controlled.
2. Description of the Prior Art
The plating of nickel metal on a variety of metals by chemical reduction methods is well known to the art. Examples of patents disclosing such chemical processes are given below:
______________________________________ U.S. Pat. No. Title Issue Date ______________________________________ 2,532,283 Nickel Plating by December 5, 1950 Chemical Reduction 2,658,839 Process of Chemical November 10, 1953 Nickel Plating 2,658,841 Process of Chemical November 10, 1953 Nickel Plating and Bath therefor 2,658,842 Process of Chemical November 10, 1953 Nickel Plating and Bath therefor 2,694,019 Processes of Chemical November 9, 1954 Nickel Plating and Baths therefor 2,762,723 Processes of Chemical September 11, 1956 Nickel Plating and Baths therefor 2,766,138 Processes of Chemical October 9, 1956 Nickel Plating 2,822,294 Chemical Nickel Plating February 4, 1958 Processes and Baths therefor 2,837,445 Continuous Processes June 3, 1958 of Chemical Nickel Plating 2,874,073 Methods of Chemical February 17, 1959 Nickel Plating 2,999,770 Process of Chemical September 12, 1961 Nickel Plating and Baths therefor ______________________________________
The above patents all describe various aqueous bath compositions containing, inter alia, a soluble nickel salt and an alkali metal hypophosphite, as well as methods for treating metal materials by immersing the metal materials in the baths.
Treatment times disclosed in the above patents range from about thirty minutes to six hours, with some plating tests being carried out in ten minutes or more.